The ECG (electrocardiogram) of a patient may be used to diagnose various problems with the patient's heart. In the context of sudden cardiac arrest, the ECG can be used to determine if the patient is in fibrillation, and, if so, if the patient's heart is susceptible to defibrillation. Using the ECG, a doctor or an AED (automatic external defibrillator) can determine whether the ECG signal represents a normal sinus rhythm or an abnormal rhythm that may be reset by administration of a defibrillating shock. The ECG signal is subject to several sources of noise. ECG signals are currently processed with digital filters to reduce noise due to other physiological sources (muscles, EGG, EMG, etc.), and nearby electrical equipment.
Halperin, et al., ECG Signal Processor and Method, U.S. Pat. No. 6,865,413 (Mar. 22, 2005) disclosed an ECG processing system which eliminates noise caused by the chest compression provided by a rescuer or chest compression device. The system includes ECG sensors (electrodes) for measuring the ECG signal of a patient, an accelerometer for producing an acceleration signal indicative of the displacement of a chest of a patient, and a processor operatively connected to the accelerometer and to the ECG sensor. The processors uses the acceleration signal to identify noise in the ECG signal. The processor processes the acceleration signal and the measured ECG signal to produces an output comprising an estimated true ECG signal. The system and method is used in ZOLL Medical's See-Thru CPR® feature of its AED Pro® automated external defibrillators.
In addition to these noise sources, the patient may be subject to motion of a vehicle used to transport the patient to a hospital. This motion may lead to noise and artifact in the ECG signal measured from the patient. We refer to this artifact as vehicle motion artifact. This noise can substantial, and may result in a measured ECG which is too noisy to be analyzed with confidence. The noise may be caused by motion of the patient and gurney over terrain, or motion of an ambulance or other conveyance used to transport the patient. Transport can be lengthy, so that a patient cannot be properly assessed for extended periods of time. Inability to assess the ECG may lead to loss of valuable diagnostic data and failure to apply defibrillating shock when appropriate.